A 24-year-old woman complains about severe pain in the mouth, body temperature up to 38°C, indisposition. The same condition occurs periodically for several years after catching a cold. Objectively: the lips are covered with bloody crusts, there are opened bladders and erosions, covered with fibrinogenous deposit on mucous membrane of lips and cheeks that is apparently hyperemic and edematic. Hypersalivation is present. What is the most likely diagnosis?